Tape guide with wear resistant coating

ABSTRACT

A tape guide in which the corner geometry between the flanges and the hub prevents the tape from abruptly bumping the flange and in which the corner is coated with a very hard wear resistant material such as zirconium nitride, tungsten carbide, silicon nitride, chromium nitride or diamond like carbon.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is a continuation-in-part of application Ser. No. 09/643,317filed Aug. 21, 2000 entitled TAPE GUIDE WITH WEAR RESISTANT COATING.

FIELD OF THE INVENTION

[0002] The present invention relates generally to tape drives and, moreparticularly, to flanged tape guides having a wear resistant coating.

BACKGROUND

[0003] Information is recorded on and read from a moving magnetic tapewith a magnetic read/write head positioned next to the tape. Themagnetic “head” may be a single head or, as is common, a series ofread/write head elements stacked individually and/or in pairs within thehead unit. Data is recorded in tracks on the tape by moving the tapelengthwise past the head. The head elements are selectively activated byelectric currents representing the information to be recorded on thetape. The information is read from the tape by moving the tapelongitudinally past the head elements so that magnetic flux patterns onthe tape create electric signals in the head elements. These signalsrepresent the information stored on the tape.

[0004] Data is recorded on and read from each of the parallel tracks onthe tape by positioning the head elements at different locations acrossthe tape. That is, head elements are moved from track to track asnecessary to either record or read the desired information. Movement ofthe magnetic head is controlled by an actuator operatively coupled tosome type of servo control circuitry. Tape drive head positioningactuators often include a lead screw driven by a stepper motor, a voicecoil motor, or a combination of both. The carriage that supports thehead is driven by the actuator along a path perpendicular to thedirection that the tape travels. The head elements are positioned asclose to the center of a track as possible based upon the servoinformation recorded on the tape.

[0005]FIG. 1 illustrates generally the configuration of a tape drive 10typical of those used with single spool tape cartridges. Referring toFIG. 1, a magnetic tape 12 is wound on a single supply spool 14 in tapecartridge 16. Tape cartridge 16 is inserted into tape drive 10 for readand write operations. Tape 12 passes around a first tape guide 18, overa magnetic read/write head 20, around a second tape guide 22 to a takeup spool 24. Head 20 is mounted to a carriage and actuator assembly 26that positions head 20 over the desired track or tracks on tape 12. Head20 engages tape 12 as tape 12 moves across the face of head 20 to recorddata on tape 12 and to read data from tape 12. Tape guides 18 and 22 maybe either roller guides or fixed guides. A conventional roller guide isshown in FIGS. 2-5. Referring to FIGS. 25, roller guide 28 includes discshaped flanges 30 and an annular hub 32. Flanges 30 and hub 32 may bemachined as a single integral part or as three separate parts bondedtogether. In either case, flanges 30 function to keep tape 12 at theproper angle as it passes across head 20. If the tape is presented tothe head at too great an angle, then the read and write elements in thehead may be misaligned to the data tracks. Flanges 30 are also needed tohelp keep tape 12 properly packed on take up spool 24.

[0006] As shown in the detail of FIG. 5, conventional guides have asquare corner 34 at the intersection of hub 32 and flange 30. Corner 34is usually formed at 90° or slightly greater than 90° (as indicated byangle θ in FIG. 5). If corner 34 is greater than 90°, then a small flatarea 36 is often used to make it easier to measure the spacing betweenflanges 30 at corner 34. Also, because it is difficult to make aperfectly square corner, a small undercut 35 is often machined into thecorner of conventional guides to ensure a flat flange surface ispresented to the tape at corner 34.

[0007] As the tape is pulled over the guides, a film of air is createdbetween the outside surface 33 of hub 32 and tape 12. This film is oftenreferred to as an air bearing. The air bearing allows the tape to movewith low friction very rapidly between flanges 30. Consequently, highfrequency tape movement can occur when the edge of the tape bumpsabruptly against the flanges 30 at corner 34. The read/write headpositioning systems have difficulty following such high frequency tapemovement.

[0008] U.S. patent application Ser. No. 09/510,834 discloses a tapeguide in which the corner geometry between the flanges and the hubprevents the tape from abruptly bumping the flange. The tape guide ofthe '834 application, which is incorporated herein by reference in itsentirety, includes a hub, a pair of spaced apart parallel flangesextending out from the hub and a corner defining the intersection of thehub and each flange. The corners are configured to apply progressivelymore force to the edge of the tape as the tape moves around the cornerfrom the hub toward the flange. For example, in one version of the tapeguide of the '834 application shown in FIG. 9, the corners are rounded.These corner configurations are designed to urge the tape more gentlyaway from the flange at a much lower rate of acceleration. Guiding thetape in this manner allows for smoother movement of the tape which inturn allows the head positioning system to better follow the tape as itwanders back and forth between the guide flanges.

[0009] As shown in FIG. 11, the edge of the tape rides on the roundedcorner of this new tape guide roller. Since the edge of the tape issomewhat abrasive, it may tend to wear the corners of the roller. Thisabrasive characteristic is more pronounced with unused tape because theslitting operation used to form the tape leaves the corner of the newtape relatively sharp.

[0010] As shown in FIG. 5 and described above, most conventional tapeguide rollers have a small undercut or “relief” machined into thecorner. Conventional rollers are usually made from aluminum with anelectroless nickel coating. Aluminum is used because it is easilymachined to a good surface finish and it is inexpensive. Electrolessnickel coating is much harder than aluminum and protects the surfaceagainst wear and corrosion. The nickel coating provides adequateprotection for conventional rollers since the edge of the tape does notride up on the corner. It has been observed, however, that nickelcoating on the new rounded corner rollers of the '834 application wearsmore quickly than is desirable. As the nickel coating wears the roundedcorner, the tape may begin to bump more abruptly against an edge oredges worn into the corner.

SUMMARY

[0011] Accordingly, the present invention is directed to a tape guidelike that described in the '834 application in which the corner regionis coated with a very hard material such as zirconium nitride, tungstencarbide, silicon nitride, chromium nitride or diamond like carbon. Eventhin coatings of such materials can be formed to exhibit a surfacehardness greater than 10 gigaPascals (GPa). It is expected that coatingmaterials applied to the roller that exhibit a hardness of at least 10GPa will be sufficient to withstand tape wear in the corners of theroller for tape materials currently used in the manufacture of magneticdata storage tapes.

DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a top down plan view of a single spool tape drive.

[0013]FIGS. 2 and 3 are plan and elevation views of a conventionalroller tape guide.

[0014]FIG. 4 is a cross section view of the roller guide of FIGS. 2 and3 taken along the line 4-4 in FIG. 3.

[0015]FIG. 5 is a detail cross section view of the corner between theflange and the hub of the roller guide of FIG. 4.

[0016]FIGS. 6 and 7 are plan and elevation views of a roller tape guideconstructed according to one embodiment of the present invention.

[0017]FIG. 8 is a cross section view of the roller guide of FIGS. 6 and7 taken along the line 8-8 in FIG. 7.

[0018]FIG. 9 is a detail cross section view of the corner between theflange and the hub of the roller guide of FIG. 8 in which the corner isrounded.

[0019]FIG. 10 is a detail cross section view of the corner between theflange and the hub of the roller guide of FIG. 8 in which the corner ischamfered.

[0020]FIG. 11 is a more detailed view of the corner shown in FIG. 9illustrating the tape moving around the corner.

DETAILED DESCRIPTION

[0021] As noted above, FIG. 1 illustrates generally the configuration ofa tape drive 10 typical of those used with single spool tape cartridges.Referring again to FIG. 1, a magnetic tape 12 is wound on a singlesupply spool 14 in tape cartridge 16. Tape cartridge 16 is inserted intotape drive 10 for read and write operations. Tape 12 passes around afirst tape guide 18, over a magnetic read/write head 20, around a secondtape guide 22 to a take up spool 24. Head 20 is mounted to a carriageand actuator assembly 26 that positions head 20 over the desired trackor tracks on tape 12. Head 20 engages tape 12 as tape 12 moves acrossthe face of head 20 to record data on tape 12 and to read data from tape12. Tape guides 18 and 22 may be either roller guides or fixed guides.

[0022] Roller guides constructed according to the present invention areshown in FIGS. 6-11. The innovative features of the invention areillustrated in the corner structures shown in the detail views of FIGS.9-11. The details of these new corner structures are not apparent fromthe smaller scale views of FIGS. 6-8. Referring first to FIGS. 6-8, eachroller guide 38 includes disc shaped flanges 40 and an annular hub 42.Tape 12 rides on the outer surface 44 of hub 42. Each flange 40 extendsradially past outer surface 44 of hub 42. When roller guide 38 isinstalled in tape drive 10, for example as guides 18 and 22 in FIG. 1,hub 40 rotates on a fixed pin or axle that extends from the tape drivechassis or other suitable support through the center of hub 40. Ballbearings or like are preferred to reduce friction and minimize wearbetween hub 40 and the pin or axle on which it turns. Fixed guides donot rotate and the hub of a fixed guide may be any shape necessary ordesired to provide a suitable guiding surface for tape 12. Flanges 40and hub 42 may be machined as a single integral part or as separateparts bonded together.

[0023] Referring now to FIG. 9, hub 42 and flanges 40 come together at arounded corner 48. In this embodiment, rounded corner 48 is a circularcurve having a radius in the range of 0.03 mm to 0.5 mm. Preferably,corner 48 transitions to a short flat area 50 on the inside face 52 offlanges 40 and then inside face 52 flares up at an angle θ to outsideedge 54 of flanges 40. Flare angle θ is typically in the range of 0.5°to 10°. Because the corner radius is usually quite small, a flat area 50makes it easier to measure the spacing between flanges 40 at corners 48.A thin coating 55 of a very hard material is applied to outer surface 44of hub 42 at least covering corner 48. Although coating 55 is onlynecessary for wear resistance at corner 48, coating 55 will typically beapplied to the entire outer surface 44 of hub 42 and the inside face 52of the flanges 30. Coating 55 should have a hardness of at least 10 GPato adequately withstand the abrasiveness of new tapes. It is expectedthat coating 55 applied to a thickness of 1 μm-3 μm will be sufficientfor most roller type tape guides to provide adequate wear resistance forthe useful life of the guide. A thicker coating may be required forstationary tape guides. Suitable coating materials include zirconiumnitride, tungsten carbide, silicon nitride, chromium nitride and diamondlike carbon. Zirconium nitride is the presently preferred coatingmaterial.

[0024]FIG. 11 illustrates the edge of tape 12 in rounded corner 48.Rounded corner 48 functions much like a spring—as tape 12 moves aroundthe progressively steeper corner 48 on coating 55 toward flange 40,progressively more force is created to push tape 12 away from flange 40.Hence, tape 12 does not abruptly bump flange 40. Instead, tape 12 ismore gently pushed away from flange 40.

[0025] Increasing the tape to flange clearance slightly over that ofconventional square corner guides should help help keep tape 12 fromriding continually on rounded corners 48. The spacing between flanges,that is to say the distance between the inside surfaces of the flangesmeasured from corner to corner, is slightly larger than the width of thetape. Hence, there is a clearance between the tape and the flanges thatallows the tape to pass unimpeded between the flanges. For example, for½ inch type data storage tapes that have a nominal tape width of 12.650mm, it is expected that increasing the tape to flange clearance by 0.01mm 0.02 mm (10-20 microns) over the clearance of a square corner guidewill be effective to help keep tape 12 off rounded corners 48. Hence, atypical square corner tape to flange clearance of 0.02 mm would beincreased to 0.03 mm-0.04 mm in a comparable tape guide that uses thenew rounded corner. This is only one example, however. The necessary ordesirable clearance may be effected by the size of the corner radius orother corner geometry, tape width and thickness and other operatingparameters.

[0026] Although a circular curve having radii in the range noted abovewill effectively reduce high frequency transient tape movement caused bythe tape abruptly bumping flange 40, it is expected that other radii orother corner configurations will also help reduce this type of transienttape movement. For example, a radii as small as 0.01 mm should providesome beneficial effect. The chamfered corner 56 illustrated in FIG. 10should also help reduce transient tape movement. Referring to FIG. 10,hub 42 and flange 40 intersect at a rectilinear corner 56 which, in thisembodiment, is a 45° chamfer. Other configurations are possible. What isimportant is that each corner be configured to apply progressively moreforce to the edge of the tape as the moves around the corner from thehub toward the flange. Also, while it is expected that the desired wearresistance will be achieved by applying a thin coating of very hardmaterial to the corners of the guide, the desired wear resistance couldbe achieved by coating the entire surface of the hub or forming theentire guide from a suitably hard material. Other configurations mightalso be possible. It is to be understood, therefore, that othervariations of and modifications to the embodiments shown and describedmay be made without departing from the spirit and scope of the inventionwhich is defined in following claims.

What is claimed is:
 1. A tape guide, comprising a hub, spaced apartparallel flanges extending out from the hub and a corner defining theintersection of the hub and each flange, the tape passing over the hubbetween the flanges, each corner configured to apply progressively moreforce to an edge of the tape as the edge of the tape moves around thecorner from the hub toward the flange and each corner having a surfaceformed of zirconium nitride, tungsten carbide, silicon nitride, chromiumnitride or diamond like carbon.
 2. The tape guide of claim 1, whereinthe surface of each corner comprises a coating of zirconium nitride,tungsten carbide, silicon nitride, chromium nitride or diamond likecarbon.
 3. The tape guide of claim 1, wherein the corner is rounded. 4.The tape guide of claim 1, wherein the corner is chamfered.
 5. The tapeguide of claim 2, wherein the coating is 1 μm-3 μm thick.
 6. The tapeguide of claim 3, wherein the rounded corner comprises a circular curvehaving a radius in the range of 0.03 mm to 0.05 mm.
 7. A tape guide,comprising a hub, spaced apart parallel flanges extending out from thehub and a corner defining the intersection of the hub and each flange,the tape passing over the hub between the flanges, each cornerconfigured to apply progressively more force to an edge of the tape asthe edge of the tape moves around the corner from the hub toward theflange, and each corner having a zirconium nitride surface.
 8. The tapeguide of claim 7, wherein the surface of each corner comprises a coatingof zirconium nitride.
 9. A tape guide, comprising a hub, spaced apartparallel flanges extending out from the hub, a rounded corner joiningthe hub and each flange, and each corner having a surface formed ofzirconium nitride, tungsten carbide, silicon nitride, chromium nitrideor diamond like carbon.
 10. The tape guide of claim 9, wherein therounded corner comprises a circular curve having a radius in the rangeof 0.03 mm to 0.5 mm.
 11. A tape guide, comprising a hub, spaced apartparallel flanges extending out from the hub, and a rounded corner havinga zirconium nitride surface joining the hub and each flange.
 12. A tapedrive, comprising: a read/write head; an actuator operatively coupled tothe head, the actuator configured to move the head in a directiongenerally perpendicular to the direction of motion of the tape over thehead; a tape guide disposed near the head, the tape guide comprising ahub, spaced apart parallel flanges extending out from the hub and acorner defining the intersection of the hub and each flange, the tapepassing over the hub between the flanges, each corner configured toapply progressively more force to an edge of the tape as the edge of thetape moves around the corner from the hub toward the flange and eachcorner having a surface formed of zirconium nitride, tungsten carbide,silicon nitride, chromium nitride or diamond like carbon.
 13. A tapedrive, comprising: a read/write head; an actuator operatively coupled tothe head, the actuator configured to move the head in a directiongenerally perpendicular to the direction of motion of the tape over thehead; a tape guide disposed near the head, the tape guide comprising ahub, spaced apart parallel flanges extending out from the hub, a roundedcorner joining the hub and each flange, and each corner having a surfaceformed of zirconium nitride, tungsten carbide, silicon nitride, chromiumnitride or diamond like carbon.